Shaft Strut Corroded

Discussion in 'Metal Boat Building' started by WaterDog, Apr 17, 2008.

  1. WaterDog
    Joined: Nov 2007
    Posts: 11
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    Location: Dallas Bluff, GA

    WaterDog Junior Member

    Hi All,
    First off I wanted to say hi and formally introduce myself to you guys.

    My name is Paul Cottrell and a couple years ago I became the proud owner of a 42 Steel Cutter named Pearl. I have started a site that I plan to keep up with stories and pics of my experience as I go through a total refit in case you want to check it out.

    My first question is in regard to my propeller shaft strut.

    Seems that there isn't much left of the strut and I will be addressing that (among other things) when she goes on land for a few months this summer.

    pics - strut photos are the 4th and 5th row down. This link is to a set of thumbnails and I warn that the full size photos are hi res but you can really see what the deal is.

    By the looks of it - how concerned should I be?

    I will need to motor a fair amount to get her to the boatyard. My plan was to run her down teh coast from Sapelo Sound to The St. Mary's, possibly the St, John's river, sailing as much as possible to save the motoring for when absolutely necessary.

    I also believe that the strut is too far forward and should be relocated farther back towards the prop. Any Advice on this?

    Do I get my welder/fabricator to fabricate one or is there a place to buy weld on struts? (Haven't been able to sucessfully find one through web searches).

    Could I / should I use a bolt on?

    I am planning to have a professional welder do some plating repairs and install some new supports on the interior for a new cockpit plan - but I wanted to know what to look for and make sure I take the correct approach.

    I've been lurking on the forums here for quite some time and am so impressed by the body of knowledge here. You all have given me great confidence that my vessel is not only worthy of a refit but will make a fine sailing yacht when I'm done.

    Look forward to participating here - thanks!

  2. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    Well, first of all, welcome to, Paul :)

    Now, I'm not an expert so don't take my advice on this matter as such. Undoubtedly, someone who has seen this before will chime in.

    It's hard to tell through all the fouling and damaged paint, but it looks as if your P-bracket (that strut holding the shaft just ahead of the prop) is itself a custom or semi-custom weldment. It is hard to ascertain its integrity from the photos; it may be OK for a while yet, but I don't think I would trust the boat to it in an offshore storm. A good machinist/welder may be able to turn a new steel tube for the cutless bearing (or find one) and make a suitable strut to hold it; I wouldn't count on finding a stock one that would fit.

    As for its location, it is quite possible and common for a fairly long length of prop shaft to be cantilevered out past the cutless bearing. There are a few relatively simple engineering calculations that should be done to ensure the shaft can be cantilevered like that without risking vibration problems or metal fatigue.

    I am trying to figure out where on Earth your zinc anodes are. Properly sized and mounted zincs are pretty important if you want the running gear to have any significant lifespan.

    Getting that underside cleaned up a bit and getting a new coating on it will go a long way towards halting the corrosion that is about to run rampant through your craft.
  3. WaterDog
    Joined: Nov 2007
    Posts: 11
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    Location: Dallas Bluff, GA

    WaterDog Junior Member

    I've done a second thorough scraping of the entire hull again this past February. (on the sandbar again). I pinged every square inch with the edge of my heavy scraper, especially the suspect spots. I found and patched 3 small holes in the plating which I patched with a ss nut-bolt-washer-epoxy putty system. Seems like the location of the problem areas coincides with where she sat on stands when on the dry.

    Right now I've got 2 large "grouper" Zincs hanging off the backstay bracket that is welded to the hull. One of them is an actual grouper zinc that I installed the day I took possesion of her and the other is a homemade one I made from a very large shaft zinc and some 1/8 inch ss cable - installed in Feb. The first grouper is about 65% gone - over about 1 1/2 years - so I guess I'm doing alright in the electrolosis dept. There is also now a zinc on that shaft.

  4. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    Hi, Paul,

    Welcome aboard.

    I tried to open both of your links just now, and got a message "internal server error". Says it is the server hosting your website.

    Could be my isp also; I'll try again tomorrow. BTW, Matt's observations are pretty good. Nice thing about a steel hull is that good grinding and welding can repair most problems.

    Regarding the strut, my personal experience is that most bolt ons are bronze, intended for wood or frp hulls. Shouldn't be too difficult to have another steel piece fabricated.
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